The plankton were found on the surface of the ISS during a routine spacewalk (Picture: Nasa/Reuters)

It may not be aliens, but an unlikely form of life has been found existing in space: sea plankton.

Russian space officials confirmed traces of the plankton and other micro-organisms living on the exterior of the International Space Station, and it appears they’ve been there for quite some time.

Cosmonauts Olek Artemyev and Alexander Skvortsov made the find during a routine spacewalk around the ISS, where they collected samples from the station’s surface, according to Russian news agency ITAR-TASS.

Later examination with high-tech equipment revealed the samples to contain the microscopic organisms, but the team say the plankton was not carried there at launch.

The team say the plankton were not carried from the blast-off location in Kazakhstan (Picture: AP Photo)

‘Plankton in these stages of development could be found on the surface of the oceans,’ said Head of the ISS mission Vladimir Solovyev.

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‘This is not typical for Baikonur [the Kazakhstani blast-off location].

‘It means that there are some uplifting air currents which reach the station and settle on its surface.’

The organisms were able to survive in the vacuum of space, despite zero gravity, freezing temperatures, lack of oxygen and cosmic radiation.